The invention relates to electric machines of the type comprised of a flux-return yoke, a plurality of segmental permanent-magnet stator magnets mounted in the yoke with their outer peripheral surfaces engaging the inner peripheral surface of the flux-return yoke, and a wound rotor mounted for rotation in the space defined by the segmental stator magnets.
Conventionally, the outer peripheral surfaces of such segmental stator magnets are smooth and are cemented or clamped to the inner peripheral surface of the flux-return yoke. If clamping is employed then, in consequence of the complete surface-to-surface contact between the segmental magnets and the yoke, there is an intensive transmission of magnetic forces from the segmental stator magnets to the yoke, and accordingly to the mounting elements of the motor construction. Furthermore, the use of clamping means involves considerable expense with respect to both material and assembly work, increasing the cost of such a machine. In addition, the clamps employed form a parallel path for magnetic flux as a result of which the useful magnetic conductivity of the motor air gap proper is reduced. Still further, electric machines built using this mounting technique very often exibit marked noise effects.
If instead of clamping, the segmental stator magnets are cemented to the inner peripheral surface of the flux-return yoke, the possibility of noise effects can be more and more reduced by employing cement layers of greater and greater thickness. However, as the thickness of the cement layer is increased, the holding action between the segmental magnets and the yoke becomes decreased, so that the motor will not meet low-vibration requirements; in that event, clamps must again be resorted to, i.e., in addition to cementing.